Background: The use of beta blockers for secondary prevention after myocardial infarction (heart attack) is supported by a solid evidence base for many ambulatory populations. However, virtually no data exist on outcomes of beta blockers in older nursing home patients, who may be particularly susceptible to adverse events from beta blockers and yield less benefit from these drugs. Aims: (1) To describe patterns and predictors of beta blocker use in older nursing home patients after myocardial infarction; and (2 and 3) to determine the impact of beta blockers on functional outcomes, rehospitalization, and death in this population. Methods: Using an observational study design that combines clinical and administrative data, the study population will comprise long-term residents in a large, national nursing home chain who were hospitalized for myocardial infarction between May 2007 and March 2010 and had not been using beta blockers prior to this event. Subjects will be followed for outcomes for 6 to 32 months after hospital discharge, comparing those who were and were not started on beta blockers after the index hospitalization. Data for this study will come from (1 the Minimum Data Set, a comprehensive database of standardized clinical assessment data that is completed at regular intervals by clinicians for nearly all nursing home residents in the United States; (2) claims data on inpatient diagnoses and services from Medicare Part A; and (3) drug utilization data from Medicare Part D and from a private nursing home chain (Manor Care), which captures drug use during periods where claims data from Part D are unavailable. Propensity score approaches and other causal inference methods will be employed to control for potential confounding in the relationship between beta blocker use and the outcomes of interest. Recognizing that no single approach can conclusively address all potential confounders, a series of estimates from related approaches will be used to converge on a clinically meaningful range of effect sizes. To further test and cross-validate results, the analyses will be repeated in two other cohorts. First, results will be analyzed for all Medicare patients nationwide who returned from hospital to nursing home without an intermediary period of post-acute rehabilitation (the period invisible to Medicare Part D). Second, analyses will be repeated for patients in VA nursing homes. VA data contain additional elements not available through Medicare, allowing testing of modeling assumptions and potential biases that can be used to refine analyses in the primary cohort. Relevance / public health significance: Better understanding the benefits and harms of beta blockers in frail nursing home residents after myocardial infarction will substantially improve the evidence base and help guide treatment decisions for this important population.